Looks like serial # 3G212185 (on passenger side pan rail)
Looks like serial # 3M340 X*423829X* (on driver's side of block under cylinder head)

X* = I can't determine if there is a digit in those locations or not--hard to read.

To the best of my knowledge:
3 = 1973; G = St. Louis, MO final assembly plant; 212185 = last six numbers of vehicle VIN

3 = 1973; M = Mound Road engine assembly plant; 4238 = engine built 03/05/1973; 29X engine built that day

fotos:
Found 340 block built March 5, 1973

Last edited by Dibbons; 06/15/16 08:41 PM.